The present invention relates to a recording/reproducing apparatus using a head drum, and more particularly to a phase-correction circuit for the recording/reproducing apparatus using a head drum.
In general, in recording/reproducing apparatuses using a head drum, such as a rotary digital audio tape recorder, a video tape recorder, etc., signals are not recorded continuously on a track of tape, but are cut and recorded in sections by a helical scanning method so that a trace start point of a head matches that of the track. This requires a drum phase servo as described below. In other words, in order to match the trace start point of the head to that of the track in which a signal is recorded, as shown in FIG. 1, a magnet is adhered to the head drum and a pulse generator detects the location of the magnet. The head is positioned at the trace start point, precisely when the magnet is detected by the pulse generator. A pulse of the pulse generator acts as a reference in forming a track during recording.
In the standard format of a digital audio tape recorder, the trace start point is located 0.6 mm from the bottom of tape. However, when a reference is not set, even if a drum is rotated at a normal speed, a track may not be formed at the center of the tape but in an upper or lower part thereof, or may even be omitted entirely.